Merge pull request #2031 from basecamp/push-subscription-race

Fix stale-read race when creating push subscriptions

app/controllers/users/push_subscriptions_controller.rb

@@ -5,13 +5,7 @@ class Users::PushSubscriptionsController < ApplicationController
   end
 
   def create
-    if subscription = @push_subscriptions.find_by(push_subscription_params)
-      subscription.touch
-    else
-      @push_subscriptions.create! push_subscription_params.merge(user_agent: request.user_agent)
-    end
-
-    head :ok
+    @push_subscriptions.create_with(user_agent: request.user_agent).create_or_find_by!(push_subscription_params)
   end
 
   def destroy

test/controllers/users/push_subscriptions_controller_test.rb

@@ -14,30 +14,12 @@ class Users::PushSubscriptionsControllerTest < ActionDispatch::IntegrationTest
     post user_push_subscriptions_path(users(:david)),
       params: { push_subscription: subscription_params }, headers: { "HTTP_USER_AGENT" => "Mozilla/5.0" }
 
-    assert_response :ok
+    assert_response :no_content
 
     assert_equal subscription_params, users(:david).push_subscriptions.last.attributes.slice("endpoint", "p256dh_key", "auth_key")
     assert_equal "Mozilla/5.0", users(:david).push_subscriptions.last.user_agent
   end
 
-  test "touch existing subscription" do
-    existing_subscription = users(:david).push_subscriptions.create!(
-      endpoint: "https://fcm.googleapis.com/fcm/send/abc123",
-      p256dh_key: "123",
-      auth_key: "456"
-    )
-
-    assert_no_difference -> { users(:david).push_subscriptions.count } do
-      assert_changes -> { existing_subscription.reload.updated_at } do
-        post user_push_subscriptions_path(users(:david)), params: {
-          push_subscription: existing_subscription.attributes.slice("endpoint", "p256dh_key", "auth_key")
-        }
-      end
-    end
-
-    assert_response :ok
-  end
-
   test "destroy a push subscription" do
     subscription = users(:david).push_subscriptions.create!(
       endpoint: "https://fcm.googleapis.com/fcm/send/abc123",